Advances in window technology have reduced energy consumption by affecting and improving heating, cooling and lighting. Various types of glass coatings have been developed for these purposes. Examples of glass coatings for reduced energy consumption include solar control coatings that reduce glare or overheating from the sun, and low-emissivity (“low-E”) coatings which reduce radiative heat losses often accounting for significant heat transfer through a window.
Low-E coatings are well known in the art. The coatings generally have a high reflectance in the thermal infrared (IR) and a high transmittance in the visible spectrum. Thus, they are low-emissive of thermal infrared. Some such coatings may admit solar near IR (NIR) to help heat a building, such as in a cold climate. Some such coatings may reflect the NIR back, such as in a warm climate. The low-emissivity optical properties are generally obtained by application of a material with certain intrinsic properties or alternatively, multiple materials may be combined to achieve the particular desired performance. One class of materials suitable for use in providing low-emissivity includes very thin films of metals. Thin films forming infrared-reflection film are generally a conductive metal such as silver, gold or copper.
Coatings including such metals can be made highly transparent to visible radiation or light, while remaining reflective in the infrared spectrum. Such infrared-reflective coatings often include one or two layers of infrared-reflection materials and two or more layers of transparent dielectric materials. The infrared-reflection materials reduce the transmission of heat through the coating. The dielectric materials allow transmission of IR and visible light and control other properties and characteristics of the coating, such as color and durability.
In order to obtain improved performance, some current systems and devices employ triple reflective metal coatings or use a barrier as an absorbing layer. By increasing the number of reflective metal layers or coatings, the infrared reflection can be increased. The industry has adopted triple silver coatings as optimal for this purpose. However, it is known that triple silver coatings suffer from color inconsistency when viewed perpendicular to the glass surface vs. at acute angles. That is, the color coordinate values of triple silver coated articles viewed from a direction that is substantially normal to the coated major surface (defined as a base view point or 0°) may be substantially different from the color coordinate values from directions that are acute to the coated major surface, such as at angles of about 10° to 89°. The shift in color coordinate values is manifested as a characteristic green or blue appearance when the coated article is viewed at an acute angle to a coated surface, for example at an angle 10° to 89° from normal to the plane of the coated surface. As the angle increases from normal, the color coordinate shift increases.
Accordingly, there is a need in the industry for a coating for a light transmissive substrate that provides improved performance and color control over currently available coatings and coated substrates while providing the infrared reflective benefits of triple metal coatings such as triple silver coatings.